Multiple choice

The pair of fair dice is rolled together till a sum of either 5 or 7 is obtained. Then , the probability that 5 comes before 7 , is :

  1. 1/5

  2. 2/5

  3. 4/5

  4. None of these
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B Correct answer
Explanation

The probability of rolling a 5 is 4/36 = 1/9. The probability of rolling a 7 is 6/36 = 1/6. The probability that 5 comes before 7 is P(5) / (P(5) + P(7)) = (1/9) / (1/9 + 1/6) = (1/9) / (5/18) = 2/5.

AI explanation

The probability of getting a sum of 5 is 4/36 or 1/9, and the probability of getting a sum of 7 is 6/36 or 1/6. The probability of 5 coming before 7 is the probability of 5 divided by the sum of the two probabilities. Therefore, the calculation is (1/9) divided by (1/9 + 1/6), which equals (1/9) divided by (5/18), resulting in 2/5.

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